Radar signal phase correction

ABSTRACT

19. In a radar circuit of the type including a transmitter section having a circuit for generating and transmitting pulsed rf oscillatory signals, a receiver section having a circuit for detecting echo signals, the combination therewith of: a means for generating a clock reference signal; means coupled to receive a portion of the pulsed rf oscillator signals generated by the transmitter and coupled to receive the clock reference signal for detecting phase differences between the transmitted signal and the clock reference signal and for generating an error signal that is proportional to a function of the detected phase differences therebetween; means coupled to receive the error signal for storing the received error signal during the interpulsed period between transmitted pulse signals; a stable local oscillator means in the receiving section for generating a c-w output signal; phase shifter means coupled to receive the stable local oscillator output signal and to receive the error signal for phase shifting the local oscillator output signal to remove phase variations in the local oscillator output signal relative to the transmitted signal resulting from rf starting phase variations in the transmitted pulses; and means for receiving the echo signals and for receiving the phase shifted local oscillator signals for producing a coherent echo signal.

United States Patent Herman et al.

[ Nov. 14, 1972 [54] RADAR SIGNAL PHASE CORRECTION combination therewithof: a means for generating a [72] Inventors: Elvin E Herman Los Angeles;Vep cloclt reference signal; means coupled to receive a mm Lym Torrance;Henry portion of the pulsed If oscillator signals generated by McCordLosAngeles, allot-Cant the transmitter and coupled to receive the clockreference signal for detecting phase difierences Assigl'leei HughesAircraft p y Culver between the transmitted signal and the clock yCalifreference signal and for generating an error signal that [22]Filed; June 21, 1965 is proportional to a function of the detected phasedifferences therebetween; means coupled to receive the PP N04 465,792error signal for storing the received error signal during theinterpulsed period between transmitted pulse [52] US. Cl ..343/ 17.1Signals; a stable local oscillamr means in the receiving 51 Int. Cl...G01s7/28,G0ls 9/02 Section for generating a Output Signal; Phase [58]Field ofSearch ..343/s DP', 7.7, 17.1', 9 shifter means coupledtofeceive the Stable local Oscil- Primary Examiner-Malcolm F. HublerAttorney-James K. Haskell and Robert Thompson EXEMPLARY CLAIM 19. In aradar circuit of the type including a transmitter section having acircuit for generating and transmitting pulsed rf oscillatory signals, areceiver section having a circuit for detecting echo signals, the

later output signal and to receive the error signal for phase shiftingthe local oscillator output signal to remove phase variations in thelocal oscillator output signal relative to the transmitted signalresulting from rf starting phase variations in the transmitted pulses;and means for receiving the echo signals and for receiving the phaseshifted local oscillator signals for producing a coherent echo signal.

19 Clairm, 10 Drawing Figures SHEEI 1 BF 6 PATENTEDMBV 14 1912 F |L kPA'TENTEDnnv 14 m2 SHEET 2 BF 6 PATENTED REV 14 1912 SHEEI 3 OF 6 Vim Nkm V NM RADAR SIGNAL PHASE CORRECTION This invention relates generallyto an improvement in radar systems and relates more particularly to ameans and a method for increasing the degree of coherence of radarreceiver output signals.

Conventional radar systems transmit pulses of rf carrier energy andreceive energy reflected from an object located within the path of thetransmitted energy. Since the reflected energy is an echo of thetransmitted energy, its rf phase is dependent upon the phase of the rfenergy at the initiation of the transmitted pulse and upon the timerequired for the energy to travel from the radar, to the reflectingobject, and back.

7 For example, if a magnetron were to be used for a transmitteroscillator, its operating characteristics are such that the first rfcycle of each main bang transmitted pulse may begin at any phase from to360 of a full rf cycle. The reflected signal returns to the radar systemwith a time delay equal to the distance from the radar to the reflectingobject and back to the radar divided by the propagation velocity of thepulse energy. Since the total phase of the reflected signal is relativeto that of the magnetron transmitter phase, the pulse-topulse phasevariations in the magnetron can affect the phase coherence of thereflected energy by as much as one full rf cycle for each received echosignal, thereby deteriorating the usefulness of the video signalinformation.

Accordingly, it is an object of this invention to provide an improvementin radar systems in which provision is made to compensate for theeffects of pulse-topulse phase variations of the transmitted rf carrierupon the reflected rf energy received by a radar system.

Another object is to provide a circuit in a system of the characterreferred to for continually referencing the phase of the transmitted rfmain bang signal and the phase of the reflected rf echo signals receivedat the radar relative to a stable reference signal.

Still another object is to provide a means in a radar system forimproving the usefulness of the video signals of a radar display circuitin a simple and novel manner.

Yet another object is to provide improvements in a conventional pulsedtype of radar circuitry.

The above and other objectives of this invention can be accomplished byemploying a radar system having a pulsed oscillator, such as themagnetron type, for the high power transmitters rf source, and includingin combination therewith, a circuit for achieving an equivalent phasecoherency between the main bang transmitted rf signal and thecorresponding received echo signals relative to a reference signal. Thesignal coherency circuit is featured by, a stable reference frequencysignal generator (clock), a phase sensor means, a memory means, and anadjustable phase shifter means.

In operation, since the phase of the main bang rf output pulse isuncorrelated from pulse-to-pulse, each transmitted pulsed rf carrier isphase-compared against a stable reference frequency signal (clock). Anerror signal having an amplitude corresponding to the instantaneousphase error between the reference signal (clock) and the main bang rfpulse signal is generated at the phase detector for each transmittedmain bang pulse. The corresponding error signal is stored in a memorymeans for one interpulse period and is applied to the phase shiftermeans to vary the phase of the highly stable reference signal (clock)accordingly. Thus, the reference signal phase is shifted withoutdisturbing the basic stability of the reference signal generator. As aresult, when an echo signal appears at the receiver output, it will haveessentially no phase component corresponding to the random startingphase of the magnetron.

During each subsequent interpulse period a new error signal is generatedwhich corresponds to the phase difference between the starting phase ofthe corresponding main bang rf carrier and the reference clock. By soutilizing the error signal, it is possible to achieve an equivalent ofphase correcting each echo signal derived from each transmitted pulse toeliminate the effects of the random starting phase differences arisingbetween the main bang rf signal and the reference signal (clock). Thus,the degree of coherence of the phase-corrected echo signals approachesthat of the reference clock within the limits of the errors of phasemeasurement and correction.

Other objects, features, and advantages of this invention will becomeapparent upon reading the following detailed description of oneembodiment and referring to the accompanying drawings in which:

FIG. 1 is a block diagram illustrating a radar circuit in which theclassical radar stages are shown in dotted line representation, and thephase correction circuit embodying the features of this invention isillustrated in solid line representation;

FIGS. 3-6 are graphs illustrating representative voltage waveforms forvoltage signals generated within the circuit of FIG. 1;

FIG. 7 is a schematic of a portion of the block diagram of FIG. 1including the reference oscillators and the phase sensitive detectors;

FIG. 8 is a schematic of a portion of the block diagram of FIG. 1including the storage circuits in boxcar detector form;

FIG. 9 is a schematic of a portion of the block diagram of FIG. 1including the phase shifter, summing circuits, and receiver phasedetector; and

FIG. 10 is an embodiment utilizing the principles of the invention.

Referring now to the drawings, a conventional radar circuit isillustrated in dotted line representation in FIG. 1. Structurally, theradar circuit includes a transmitter section and a receiver sectionwhich are electrically isolated from one another and are alternatelyconnected to an antenna 12 by means of a duplexer 13. A magnetrontransmitter 14 may be maintained at a frequency with a fraction of a Meof a prescribed nominal frequency by a feedback circuit including acavity discriminator 16 that generates an output signal having anamplitude portional to frequency variations for controlling a tuningservo 17. The magnetron tuning servo develops an output to change thefrequency of the magnetron transmitter 14. The result of this feedbackcircuit is to tune the magnetron frequency to essentially that of thecavity discriminator. It should be understood that the radar circuit isnot limited to the radar illustrated but can be of any other classicaldesign including klystron types.

In transmit operation, a main bang waveform (FIG. 2) of pulses of rfenergy is generated by the magnetron This main bang waveform can berepresented by the function:

a s t s 1- and at all other times where:

A, amplitude of i'" pulse w carrier frequency 4), random phase variation(radians) It should be understood that the graphical waveforms are notthe actual waveforms since FIG. 2 is merely intended to illustrate therandom phase variation of (1:, of the rf carrier (0 from pulse-to-pulse,and the resultant phase shift in the transmitted signal. Consequently,the graph and all subsequent graphs have been made as simple as possibleand are merely representative of the actual waveforms. The rf carrier wcan, for instance, actually be in the x-band with a carrier of 9,375.0Mc, have a pulse duration of from 0.5 microseconds to 0.15 microseconds,and an interpulse period of 5,000 microseconds. It should be understoodthat these need not be the actual values used and, in fact, they may noteven be the best values. These values have only been selected in orderto make the description as definite as possible.

Since the duplexer 13 does not provide perfect electrical isolationbetween the transmitter section and the receiver section, a portion ofthe transmitted energy leaks through the duplexer 13 and can be appliedto a mixer 21. The mixer 21 combines or heterodynes the leakage signalwith an rf signal from a stable local oscillator 22 to generate an IFsignal. This IF signal can, for example, be about 30 Me. The mixer 21can be of any classical type used in conventional radar circuits. Thelocal oscillator 22 must have sufficient short term stability topreserve phase coherence over the interpulse period. Thus, an IF signalis generated for each magnetron transmission pulse. A receiver IFamplifier stage 23 receives and amplifies the heterodyned IF output fromthe mixer 21 and feeds it to a phase-correcting circuit embodying thefeatures of this invention.

Although the mixer 21 also heterodynes a modulated echo signal g(l) atsome later time 2R/c where:

(ZR/c) s s (2R/c)+1-; and 0 at all other times where:

c propagation velocity k attenuation factor R one way range to target togenerate a modulated IF echo signal and the IF amplifier 23 alsoamplifies this modulated IF echo signal, the operation of thephase-correcting circuit will be described first since then, the reasonfor phase-correcting the main bang IF signal to eliminate the 5, randomphase variation in the transmit signal can be better understood.

The phase-correcting circuit operates generally in the following manner.The main bang IF signal output from the IF amplifier 23 is phasecompared, at two phase detectors 26 and 27 with the phases of two IFreference signals generated by a common c-w (clock) oscillator 28. Oneof these two reference signals is phased with respect to the other by a90 lag circuit 37. The resultant phase error signals from the phasedetectors 26 and 27 are video pulses having amplitudes proportional tothe sine and to the cosine of the phase difference between the comparedsignals and are stored in storage means 29 and 31, respectively, for theremainder of the interpulse period llf An advantage of this circuit isthat the reference oscillator need only be at the nominal frequency ofthe transmitter.

The stored voltage signals are each applied to an individual one of twophase shifter circuits 32 and 33 which operate to shift the phase of thetwo reference signals from the c-w (clock) oscillator 28 in proportionto the error voltages. One of these two reference signals is phaseshifted 90 with respect .to the other by a second 90 phase lag circuit.These reference signal outputs from the phase shifters 32 and 33 aresummed or added together at a summing circuit 34 and the resultantphase-shifted IF signal r( t) of FIG. 4:

or s z s l/fr;0atallothertimes where:

B amplitude of phase-corrected IF reference m IF frequency (30 Mc) a=time required to phase sense and phase correct (in main bang carrierphase variation is applied to a receiver phase detector 36 at thereceiver output. Thus, the phase of the reference signals will becontinually adjusted once each interpulse period to correspond to randomphase variations 4), in the transmitted rf carrier of the magnetron. Asa result, when the corresponding echo signal is received it will becoherent with the phase-shifted IF reference.

The advantages of phase-correcting the IF reference signal r(t) for eachtransmitted pulse f,(t) will now be explained. As previously discussed,the characteristic operation of a magnetron transmitter is such that theinitial phase d), of the rf carrier to, varies in a random manner frompulse topulse. That is, the main bang signal fi(t) could be described bythe mathematical function:

f1( 1 o +i) (1) When the main bang energy is reflected from an isolatedpoint reflector, the resultant received echo signal g(t) has a carriersignal substantially identical to the above function except with a timedelay and an amplitude decrease due to energy losses during transmissionand reflection:

generate a modulated IF output signal having the same characteristicfrequency of the phase-shifted IF c-w reference oscillator (30 Me). TheIF echo signal is then amplified by the IF stage amplifier 23 andapplied to the phase detector 36 at the receiver output. Since the RFecho signal is substantially identical to the transmitted signal butwith a time delay and change in amplitude, the IF echo signal u(t) ofFIG. 5 will be substantially in phase with the phase shifted IF c-wreference signal r(t) applied to the other input of the detector 36except for the phase component due to the time delay 2R/c and can berepresented by the functron:

and 0 at all other times Since the phase of the IF reference signal isdependent upon the RF phase of the main bang pulse most recentlytransmitted, the output s(t) (FIG. 6):

and 0 elsewhere of the receiver IF phase detector 36 will be a pulsewhose amplitude is uniquely related to the phase shift resulting fromthe time delay 2R/c but with essentially no amplitude dependence uponthe random RF phase (1:,- of the transmitter main bang output. Thus, thecoherent video output of the phase detector 36 can be used to detectminute changes in the time delay from objects of interest since the RFphase variations from successive transmitter pulses are effectivelyremoved in the output of the phase detector 36, leaving pulses whoseamplitudes are essentially independent of the random transmitter RFphase variations.

Referring now to the details of the circuit, FIG. 7 is a schematicdiagram of a portion of the block diagram of FIG. 1 illustrating thecontinuous wave reference oscillator 28, the 90 lag circuit 37, and thephase sensitive detectors 26 and 27.

The reference oscillator 28 or clock is a Colpitts oscillator having atank circuit including an inductor 52 connected at one end with aparallel pair of capacitors 54 and 56 and with a series pair ofcapacitors 58 and 60. A crystal 62 is coupled from the junction ofcapacitors 58 and 60 and an oscillator output terminal 64 to feed back a30 Mc signal to the emitter terminal of a transistor 66. In effect, thecrystal 62 maintains the oscillator operating at 30 Me. An emitter biasresistor 68 is connected between the emitter and a common terminal,whereas, base bias is provided by a resistor 70 connected between thecommon terminal and the base terminal of transistor and by a resistor 72connected between an electrical power supply input resistor 74 and thebase terminal. Bias capacitors 76 and 77 are connected to ac shunt thebase resistors for keeping the base bias constant during oscillatoroperation. It should of course be understood that the frequency of thereference oscillator output is the same as the nominal frequency of themain bang leakage signal which is also applied to the phase sensitivedetectors 26 and 27. In other words, if the main bang leakage signal isan rf signal, then the reference oscillator 28 must also be an rfoscillator of the same nominal frequency.

A 30 Mc reference signal is provided for use in the phase shifter stagesof the circuit by feeding the reference oscillator output on line 64 tothe base terminal of an emitter follower transistor 75. The 30 Mc outputsignal is developed across the emitter follower resistor 79 which isconnected at one end to a terminal at a negative voltage and to groundthrough a bypass capacitor 81. The resultant 30 Mc output on terminal'83 can thereafter be used in the phase shifting circuit in a manner tobe described in more detail later.

The 30 Mc c-w reference output from the reference oscillator 28 isprocessed into two 30 Mc signals which are shifted into phase quadraturewith one another by the 90 phase lag circuit 37. In operation, the 30 Mcsignal on output line 64 is applied to the base terminal of an emitterfollower transistor 78 and amplified. The transistor 78 has a pair ofbase bias resistors 80 and 82 connected thereto. An emitter degenerationresistor 84 is connected from the emitter terminal to a common terminalthrough a bypass capacitor 86. An emitter bias resistor 88 is connectedbetween a terminal at 15 volts dc relative to a common or groundterminal and the degeneration resistor 84. Hereafter, it should beunderstood that all voltage values are dc and relative to the common orground terminal unless otherwise identified.

The amplified 30 Mc reference signal is divided into two circuitbranches with one branch being fed to the phase sensitive detector 26and the other branch being shifted or lagged 90 in phase relative to thefirst branch signal by the operation of the 90 phase lag circuit 37 andthen applied to the phase sensitive detector 27.

In the 90 phase lag circuit 37, the 30 Mc reference input to the phasesensitive detector 27 lags 90 when fed through series inductor 90 andacross the parallel pair of capacitors 92 and 94. In effect, the 90phase shift circuit 37 can be thought of as a 1r section equivalent of adouble tuned transformer with the inductor 90 being connected across twotransformer legs which include an input transformer 96 of the phasedetector 26 and a similar input transformer (not shown) of the phasedetector 27 The parallel pair of capacitors 98 and 99 provide 30 Mctuning with the transformer 96 just as parallel pair of capacitors 92and 94 provide 30 Mc tuning with an input transformer in the detector27. In addition, a balance resistor 102 is connected in parallel acrossthe parallel pair of capacitors 92 and 94 to balance the 30 Mc referencesignal current flow in each leg of the double tuned transformer.

In addition to the 30 Mc c-w reference signals, a 30 Mc IF signalresulting from main bang leakage is also fed to the phase sensitivedetectors 26 and 27. In operation, the main bang IF signal fed to inputterminal 104 can be thought of as being a sine wave 30 Mc pulse trainhaving a duration equal to the main bang pulse duration and a startingphase corresponding to the starting phase of the main bang rf signal.This main bang leakage IF signal is fed through a series input resistor106 and across an input load resistor 108 to develop a signal which isfed through a series coupling capacitor 110 to the base terminal of acommon emitter transistor 112. The transistor 112 has a base biasresistor 114 connected from the base terminal thereof to a commonterminal. A degeneration resistor 116 is connected from the emitterterminal to ground through a bypass capacitor 118. In addition, anemitter bias resistor 120 is connected in series from the degenerationresistor 1 16 to a terminal at volts and to ground through a bypasscapacitor 122. The collector output of transistor 112 is connected to aparallel tuned LC circuit including a capacitor 122 and an inductor 124connected at one end to the collector terminal and at the other end to acommon terminal, and a resistor 126 connected between a center tap onthe inductor 24 and the common terminal. The value of these circuitcomponents is chosen so that the parallel tuned circuit is tuned to acenter frequency of 30 Me. In addition, the gain of the amplifiertransistor 112 is chosen so that the amplifier main bang IF (30 Mc)signal on output line 128 has a lower amplitude than the 30 Mc c-wreference signal.

The main bang IF signal applied to the other phase sensitive detector 27is amplified in substantially the same manner by essentially the sameamplifier circuit, just described and, as a result, the detail of thisportion of the circuit is not described in detail.

A phase sensitive diode detector 130 is connected to receive the 30 Mcreference signal and the 30 Mc IF main bang leakage signal forgenerating dc pulse signals having amplitudes proportional to the sineof the phase difference between input signals fed to the phase sensitivedetector 26 and a dc output pulse signal proportional to the cosine ofthe phase difference between input signals fed to the phase sensitivedetector 27. In operation of the phase sensitive detector 26, the 30 Mcreference signal is divided into two circuit branches with one signalbeing applied directly to one branch of the diode detector 130 andthrough a capacitor 132 while the other signal is phase shifted 180 bythe center tap input transformer 96 and is then applied to the otherbranch of the diode detector and through a capacitor 134. The 30 Mc mainbang leakage IF signal is applied to one branch of the detector 130through a diode 136 and is applied to the other branch of the detectorthrough an oppositely polarized diode 138. The two input signals fedthrough the detector branch that includes capacitor 132 and diode 136are summed by the summing resistor 140. The two input signals fedthrough the detector branch that includes capacitor 134 and diode 138are summed at the summing resistor 142. In effect, the high afnplitude30 Mc reference signal inputs cancel one another out at the junction 144since the center tap input transformer has shifted one of them 180 inphase. The resultant output at summing junction 144 is a dc pulse havingan amplitude proportional to the sine phase difference between the IFreference signal input and the IF main bang leakage signal input.

This phase difference output pulse signal at junction 144 is applied tothe base terminal of an emitter follower transistor 146 through a baseloading resistor 148. The transistor 146 has a collector bias resistor150 connected to a terminal at +15 volts and to a bypass capacitor 152which is in turn connected to a common terminal at the other end. Anemitter load resistor 154 is connected to a terminal at l5 volts and toa bypass capacitor 156 which is in turn connected to a common terminalat the other end thereof. In addition, the emitter terminal has a beadof ferrite material 158 secured therearound which acts as an rf choke. A30 Mc trap including a parallel pair of capacitors 160 connected betweena common terminal and in series with an inductor 162 is connected to thesumming junction 144 and traps any 30 Mc leakage signal.

The sine 4) phase difference signal and the cos phase difference outputsignal pulse from the phase sensitive detectors are fed to the storagecircuit of FIG. 8 at input terminals 164 and 166, respectively. Thestorage circuit of FIG. 8 includes two parallel branches each includinga video amplifier which feeds an amplified signal to a boxcar detector172 having a diode gate 174 connected so that a storage capacitor 176samples the instantaneous amplitude of the phase difference signal forvery short duration at a select pulse portion during the pulse duration,as determined by a gate pulse applied to the input terminal 180 of apulse forming circuit 182 from the radar circuit.

In operation, the sine (1) phase difference signal is applied to thebase terminal of a common emitter transistor 184 in the first stage of acascode amplifier in the video amplifier 170 through an input impedanceresistor 186. The emitter terminal of transistor 184 is ac coupled toground through a low resistance degeneration resistor 188 and a bypasscapacitor 190. An emitter bias resistor 192 is connected from thedegeneration resistor 188 to a decoupling filter including a resistor194 coupled to a terminal at a l5 volts and a capacitor 196 coupled to acommon terminal.

The collector output of transistor 184 is applied to the emittertern-iinal of a second cascode amplifier stage which includes commonbase transistor 198. This common base transistor 198 has a base biasresistor 200 connected at one end to ground and with a capacitor 202shunted thereacross. Base bias is provided to the base temiinal throughvoltage divider resistors 204 and 206 connected in series between aterminal at +15 volts and the base terminal. A collector load resistor208 is connected to the junction of voltage divider resistors 204 and206. In addition, a bypass capacitor 210 is connected from the junctionof the voltage divider resistors 204 and 206 to a common terminal toform a decoupling filter. Ferrite beads 212 and 214 are connected to theemitter terminal and to the collector terminal of the transistor 198 andact as rf chokes.

The collector terminal output of transistor 198 is fed to the baseterminals of a complementary symmetry stage having emitter followertransistors 216 and 218 which conduct the amplifier bipolar phasedifference signal sine d: through a coupling capacitor 220. Collectorbias is applied to common emitter transistor 216 through a resistor 222connected in circuit with a capacitor 224 which has the other endconnected to a common terminal. The collector terminal of common emittertransistor 218 is connected to the common terminal. In addition, thecollector terminals have ferrite beads connected thereto which operateas rf chokes. Base bias is provided for the transistor 216 by theresistors 204 and 208, and base bias is provided for the transistor 218by a resistor 226 connected at one end to the common terminal. A pair ofdiodes 228 and 230 are connected in series between the base terminals ofthe complementary symmetry transistors 216 and 218 so that transistor216 conducts positive polarity signals through an emitter load resistor232 and the transistor 218 conducts negative polarity signals through anemitter load resistor 234.

To ensure that the output line 236 leading to the boxcar detector isclamped at a constant dc reference potential to overcome the possibleeffects of long term charge-up of the circuit components, a normally OFFtransistor switch 238 is turned on and then turned off a short timebefore the phase difference pulse signal is conducted through thecoupling capacitor 220, whereby a dc reference potential is restored onthe output line 236. In operation, the clamping pulse is applied to thebase terminal of the normally OFF transistor 238 from an input terminal240 through a coupling capacitor 242, via a line 244, and through a basebias resistor 246. The dc reference level on output line 236 is thus setthrough the transistor 238 by a voltage divider including resistors 248and 250 connected in series between a negative voltage terminal andcommon terminal. The emitter terminal of normally OFF transistor 238 isconnected to the voltage divider resistor 250 which can be adjusted toset the reference voltage. Base bias is provided for the transistor 238by a resistor 252 having one end connected to the common terminal. Basebias is also provided through resistor 254 connected from the baseterminal to a common terminal through the bypass capacitor 196.

The output signal from the video amplifier 170 is applied to a diodegate 174 in the boxcar detector 172 wherein, after a predetermined timedelay, a portion of the phase difference pulse signal is sampled andstored on a storage capacitor 176. The sampling operation is controlledby a synchronized sampling pulse applied to the input terminal 180 of apulse shaping circuit 182 from the radar transmitter (FIG. 1),whereupon, very short duration gate pulse is applied to enable the diodegate 174 for the very short duration. In operation, this gate pulse isapplied to the base terminal of a normally OFF transistor 256 of ablocking oscillator through a differentiating circuit including acapacitor 258 and a resistor 259. Any negative portion of thedifferentiating pulse is clipped by a diode 261 connected between thebase terminal of the transistor 256 and a common terminal. The gatepulse turns on the transistor 256 whereby the regenerative feedbacksignal between the winding of transformer 260 connected to the emitterand to the collector is sufficient to saturate transistor 256. After ashort duration of say, 0.1 microsecond from the initial turn-on, theregenerative feedback in the emitter winding and the collector windingof transformer 260 is sufficient to turn off the transistor 256. A diode262 is connected in parallel across the collector winding of thetransformer 260 to prevent ringing of the circuit. The diode 262 and thecollector winding of transformer 260 are connected at one end to abypass network including a resistor 264 which is connected at the otherend to a volt terminal and to a bypass capacitor 266 which is in turnconnected at the other end to a common terminal. The output pulse fromthe blocking oscillator is fed to a common emitter inverter transistor268 through a coupling capacitor 270 and a voltage divider networkincluding resistors 272 and 274. A speed-up capacitor is shunted acrossthe resistor 272 and the base terminal of inverter transistor 268 isconnected to the junction of the voltage divider resistors 272 and 274.The resultant output on the collector terminal 276 is a square wavepulse having a duration of about 0.1 microsecond.

Referring now to the details of the boxcar detector 172, the output fromthe video amplifier applied to the diode gate 174 at a center tap of aninput transformer 278 is sampled and stored on capacitor 176. The oneend of the transformer of diode gate 174 is connected to a circuitbranch containing a Zener diode 280 which is back-biased and normallyconducting and a diode 282 which is back-biased and normally off. Theabove bias of these diodes is attained through a resistor 281 connectedfrom a +15 volt terminal to the junction of the Zener diode 280 anddiode 282. The other end of the input transformer winding is connectedto a branch including a Zener diode 284 which is polarized oppositely ofthe Zener diode 280 and is back-biased and normally ON and a back-biasednormally OFF diode 286. Bias for these diodes is obtained through aresistor 282 connected from a terminal at l 5 volts to the junction ofthe Zener diode 284 and diode 286. An output lead 288 is connected tothe junction of the normally OFF diodes 282 and 286.

To sample and store the phase difference signal, the signal on inputline 236 will be conducted on the storage capacitor 176 when a gatingpulse is received from the gate pulse forming circuit 182 by the primary290 of a pulse forming transformer which is in turn coupled to the inputwinding 278 of the diode gate.

In operation, the gating pulse applied to the primary winding 290produces a magnetic coupling force which generates a correspondingsignal across the secondary winding 278, causing the diodes 282 and 286to be forward-biased. As a result, the sine 4) phase difference inputpulse signal on line 236 is transferred through the conducting diode andcharges the storage capacitor 176. At the end of the 0.1 microsecondgating pulse, the diodes 282 and 286 are again backbiased, whereupon,the signal or charge stored on capacitor 176 is retained 'for theremainder of the interpulser period l/f,. The signal stored on capacitor176 is fed to the grid of a cathode follower 292 through a gridimpedance resistor 294, whereupon, the output signal generated acrossthe cathode follower resistor 296 is a dc signal and is applied to thebase terminal of an emitter follower transistor 298. The cathodefollower resistor and an emitter loading resistor 299 are connected to anegative voltage terminal, whereas, the collector terminal of transistor298 is connected to a positive voltage terminal. Thus, the boxcar outputsignal on output line 300 is a dc signal proportional to the sine of thephase difference previously detected. The boxcar output signal on outputline 301 from the other boxcar detector 172 in storage circuit 31 isalso a dc signal but is proportional to the cosine of the phasedifierence previously detected.

When the pulse forming transformer is turned off, a diode 302, connectedbetween the two primary windings 290, catches the back swing to preventthe circuit from oscillating. In addition, the diode 302 and the twoends of primary windings 290 are connected in common to a bypass circuitincluding a capacitor 304 which is connected at one end to a commonterminal and a resistor 306 which is connected at one end to a terminalat l volts.

To phase shift the c-w IF reference signal to correspond to the randomstarting phase of the main bang leakage signal, the 30 Mc referencesignal generated by oscillator 28, is applied to the input terminal 83of the phase shifter circuits 32 and 33 schematically illustrated inFIG. 9, whereas, the sine (,b phase shift signal from the boxcar 29 isapplied to input terminal 300 and the cos (1) phase shift signal fromthe boxcar 31 is applied to the input terminal 301. In operation, a pairof balanced modulators 314 each modulate a separate one of the two phasedifference signals against the phase quadrature c-w reference signalwherein the resultant output signal is summed at a summing junction 34amplified through a transformer and amplifier 315, phase detected atphase sensitive detector 318 to generate a coherent video output signalat output terminal 320.

In operation, the 30 Mc c-w reference signal is applied to the baseterminal of a common emitter amplifier transistor 322 from the inputterminal 83. The amplifier transistor 322 is base biased through voltagedividing resistors 324 connected to ground and 326 connected to aterminal at l5 volts and ac coupled to a common terminal from thenegative terminal through a bypass capacitor 328. An emitterdegeneration resistor 330 is ac connected to ground at one end through abypass capacitor 332. Emitter bias is also provided through the emitterdegeneration resistor 330 from a bias resistor 334 having one endconnected to a terminal at l 5 volts.

The amplified output signal on the collector terminal 336 is applied toa 90 phase lag circuit 40. The 90 phase lag circuit 40 divides theamplified 30 Mc reference signal into two 90 out-of-phase referencesignals or phase quadrature reference signals. Since the 90 phase lagcircuit 40 is essentially identical to the phase lag circuit 37illustrated in FIG. 7, it is not described in detail and is thusrepresented in block diagram form.

One output from the phase lag circuit 40 is applied to the balancedmodulator 314 of phase shifter circuit 32 and is modulated against thesine phase shift signal from the associated boxcar circuit 172. The 90phase shift output signal is applied to the balanced modulator 314 ofphase shifter circuit 33 and is modulated against the cosine (I) phaseshift signal from the associated boxcar circuit 172.

Referring now to the details of the operation of balanced modulator 314,the 30 Mc input signal is applied to a split, center-tapped winding 338to generate two 180 out-of-phase reference signals on a centertappedsecondary winding 340. Each half of the primary 340 has an impedanceresistor 342 connected in parallel across it and to the center-tappedcommon terminal. Each branch of the balanced modulator includes a seriestuned LC circuit including capacitor 344 and inductor 346 in one branchand inductor 348 and a pair of parallel capacitors 350 in the other leg.These series tuned LC circuits are each tuned to 30 Mc. Each seriestuned circuit is connected to an output summing junction 34 through adiode 352 in one branch and oppositely polarized diode 354 in the otherbranch. These two diodes are biased so that they are normally on whenzero volt sine input signal is applied to them through the'chokes 356and 358; or in other words, when the phase shift signal sine dz on inputterminal 310 is zero volts. When, however, the diodes are biased by theinput signals sine ()5 they conduct at different voltage levels.

The balanced modulator 314 illustrated in block diagram form alsooperates on the preceding general principle. Consequently, since theinput 30 Mc input signal to modulator 314 for out-of-phase to the inputsignal to modulator 314, the diodes conduct at different voltage levels,whereupon the total output signal to the summing junction 34 is a phaseshifted 30 Mc sine wave. In other words, the signal at summing junction34 is phase shifted radians, which correspond to the random rf startingphase of the main bang pulse.

Bias is provided for the diode 352 through the adjustable voltagedividers 360 and 361 for both balanced modulators 314. Bias is providedfor the diode 354 in both modulators 314 by the resistors 364 and 365which are connected at one end to a negative voltage and to a commonterminal through a bypass capacitor 366. Impedance resistors 368 and 370provide the voltage drop of the boxcar input signals on terminals 310and 312 which vary the bias level on the diodes in each balancedmodulator.

The phase shifted 30 Mc signal is amplified in a three-windingtransformer 372 and is then applied to the amplifier 315 through acoupling capacitor 374. An

impedance resistor 376 is shunted across the primary input winding ofthe transformer 372.

The amplifier 315 further amplifies the phase shifted IF referencesignal to a usable level for a phase sensitive detector 318. Theamplifier 315 is illustrated in block diagram form since it operates onthe same general principle as the Ycascode amplifier portion of thevideo amplifier 170 illustrated in FIG. 8, with the exception that thecomplementary symmetry circuit is replaced with a conventional commonemitter transistor stage.

The 30 Mc phase shifted signal is applied to the base terminal of acommon emitter transistor 380 through a coupling capacitor 382 where itis further amplified. Base bias is provided through a resistor 384connected to ground and a resistor 386 which is ac connected to groundthrough a bypass capacitor 388. An emitter degenerator resistor 390 isconnected to ground through a bypass capacitor 392. Emitter bias isprovided for transistor 380 through an emitter bias resistor 394. Thisamplified 30 Mc phase shifted signal developed on the collector terminalis applied to the phase sensitive detector 318 where it is phasecompared with the IF echo signal received on input terminal 320.

Phase sensitive detector 318 operates on substantially the sameprinciple as the phase detector illustrated in FIG. 7 and thus isillustrated in block diagram form. In operation, a variable capacitor400 is used to tune the input winding to 30 Me. In addition, a feed backcapacitor 402 is connected from the detector to the base terminal of thecommon emitter transistor 380 to eliminate the Miller effect therein. Inoperation, the

30 Mc echo signal is applied to the detector 318 through an impedancematching 1r network 404. The output terminal 406 of phase sensitivedetector 318 is connected across a 30 Mc trap including an inductor 408and a capacitor 410, wherein the resultant output terminal 412 of thephase sensitive detector 318 is a video pulse having a variableamplitude dependent upon the phase difference between the phase shiftedreference signal and the IF echo signal. Since the reference signal hasbeen phase shifted to correspond to the random starting phase of themain bang pulse its phase relationship to the echo signal will beconstant except for the two-way time delay 2R/c between the antenna andthe target. Thereafter, the coherent video output can be furtheramplified and processed for a conventional video display.

Another embodiment illustrated in FIG. is arranged to compare the randomstarting phase variation between the main bang rf signal and c-wreference signal (clock) generated by a reference oscillator 425operating at the same rf level of the transmitter 17. The operation ofthe radar transmitter portion is substantially identical to theoperation of the corresponding portions of the preceding embodimentillustrated in FIG. 1. That is, the transmitter 14 generates a main bangpulse f(z). This main bang pulse flt) is conducted through the duplexer13 and radiated into space by the antenna 12. The transmitter 14 ismaintained to within a fraction of a Me of a predetermined rf frequencyby an afc feedback loop including the cavity discriminator l6 and thetuning servo 17 connected to correct the frequency of the transmitteroutput signal.

Referring now to the phase correction portion of the circuit, the mainbang rf signal from the transmitter 14 is phase compared with the c-wreference signal from the reference oscillator in a phase detector andstorage circuit 428. The reference oscillator 425 operates insubstantially the same manner as the reference oscilla tor 28schematically illustrated in FIG. 7, except that it is set to operate inthe rf frequency of the transmitter 14.

The phase detector and storage circuit 428 operate in substantially thesame manner as the phase sensitive detector and the storage circuitillustrated in FIGS. 7 and 8, in that the main bang signal and thereference signal (clock) are phase detected in phase quadrature,whereupon a sine d and a cosine d: phase difference signal are generatedand applied to a phase shifter 430 or to a phase shifter 432. It shouldbe understood that if phase shifter 430 is used, phase shifter 432 isomitted, and the local oscillator is connected directly to the mixer 21.Conversely, if the phase shifter 432 is used, phase shifter 430 isomitted, and the duplexer 13 is connected directly to the mixer 21.

The phase shifters 430 and 432 operate on substantially the sameprinciple as the phase shifters illustrated in FIGS. 1 and 9, exceptthat they are set to operate at the rf level. In addition to this phaseshifter, it is practical, under certain circumstances, to use a ferritemodulator of the type described in U.S. Pat. No. 3,084,295, issued onApr. 2, 1963, to H. A. Rosen and entitled Ferrite Modulators forDeviating Magnetrons for the phase shifters 430 and 432.

Referring now to the operation of the phase shifter 430, the sine andthe cosine 4 phase difference error signals are applied to the phaseshifter 430 for the interpulse period. As a result, when the echo signalg(r) is received and conducted through the duplexer 13 to the phaseshifter 430, the phase shifter 430 operates to phase shift the echosignal in accordance with the amplitudes of the phase difference errorsignals sine d: and cosine 4:. Since the amplitudes of the sine d) andcosine dz signals are dependent upon the random rf starting phasevariation qb of the main bang pulse, the echo signal g(t) will be phaseshifted so as to eliminate the random phase variation component #2 inthe echo signal. Thereafier, this operation is continually repeated foreach subsequent main bang pulse, whereupon, no starting phase variationappears in the echo signal fed to the mixer 21.

Thus, when the signal from the stable local oscillator 22 is heterodynedagainst the echo sign al in mixer 21, the resultant IF signal applied tothe receiver IF stage 23 and the receiver phase detector 36 always hasthe same phase relative to an IF reference signal generated by thereference oscillator 28 except for phase variations due to the two-waytime delay to the target 2R/c. Consequently, the video output signal onterminal 428 has an amplitude that is proportional to phase variationsclue to variations in target range only and is thus a coherent videosignal.

In the embodiment where phase shifter 430 is omitted, phase shifter 432shifts the c-w output signal from the stable local oscillator 22 inaccordance with the magnitudes of the phase difference error signalssine (b and cosine d) for shifting the phase of the local oscillatoroutput signal to remove phase variations in the local oscillator outputrelative to the main bang signal resulting from rf starting phasevariations in the main bang pulses. As a result, when the echo signalg(t) is fed to the mixer 21, it is heterodyned against a stable localoscillator signal which is phase shifted to eliminate the randomstarting phase variation (1) relative to the corresponding echo signal.Consequently, the IF output signal fed to receiver IF stage 23 andreceiver phase detector 36 has no random phase variation component d)and, thus, always has the same relative phase relationship to the IFclock signal from reference oscillator 28 except for those phasevariations resulting from the two-way time delay to the target 2R/c.

In addition, the principles of the phase correction technique can alsobe utilized in other combinations such as: phase detecting and measuringat the rf frequencies and phase shifting the echo signal at the IFfrequencies; and phase detecting and measuring at the IF frequencies;and phase shifting the echo signal at IF frequencies.

Since the receiver stage components are substantially identical to thereceiver stage components illustrated in FIG. 1, they are given the samereference characters throughout, and thus, are not described in detail.

While salient features have been illustrated and described with respectto a particular embodiment, it should be readily apparent thatmodifications can be made within the spirit and scope of the invention,and it is therefore not desired to limit the invention to the exactdetails shown and described.

What is claimed is:

1. In a radar circuit of the type including a transmitter section havinga circuit for generating and trans mitting a pulsed rf oscillatingsignal, a receiver section having a circuit for receiving and detectingecho signals, and means for connecting the transmitter section to andthe receiver section to an antenna means, the combination therewith of:a stable oscillator means for generating a reference signal; meanscoupled to receive a portion of the transmitter rf signals and coupledto receive the reference signal for measuring phase differencestherebetween and generating an error signal proportional to a functionof the measured phase differences; and means coupled to receive thereference signal and to receive the error signal for phase shifting thereference signal in proportion to the error signal for removing phasevariation between the reference signal and the transmitted" pulseresulting from starting phase variations in the transmitted signalwhereby the reference signal is made coherent relative to each relatedecho signal.

2. In a radar circuit of the type including a transmitter section havinga circuit for generating and transmitting a pulsed rf oscillatingsignal, a receiver section having a circuit for receiving and detectingecho signals, and means for connecting the transmitter section to andthe receiver section to an antenna means, the combination therewith of:a means for generating a clock reference signal; means coupled toreceive a portion of the transmitter rf signals and coupled to receivethe clock reference signal for detecting phase differences between thetransmitted signal and the clock reference signal and for generating anerror signal that is proportional to a function of the detected phasedifferences therebetween; and means coupled to receive the referencesignal and to receive the error signal for phase shifting the referencesignal in proportion to the error signal for removing phase variationbetween the clock reference signal and the transmitted pulse resultingfrom starting phase variations in the transmitted signal whereby thereference signal is made coherent relative to each related echo signal.

3. In a radar circuit of the type including a transmitter portion havinga circuit for generating and transmitting main bang pulses having an rfcarrier, a receiver portion having a circuit for receiving echo signals,and means for coupling the transmitter portion to and the receiverportion to an antenna means, the combination therewith of: a stableoscillator for generating a reference signal; means coupled to receive aportion of the transmitter signals and to receive the reference signalfor detecting phase differences therebetween and for generating an errorsignal that is proportional to a function of the detected phasedifferences; means coupled to receive the error signal for storing thereceived error signal for a time period; and means coupled to receivethe reference signal and to receive the stored error signal for phaseshifting the reference signal in proportion to the error signal toremove phase variations in the reference signal relative to thetransmitted signal whereby the reference signal is made coherentrelative to each related echo signal.

4. In a radar circuit of the type including a transmitter portion fortransmitting main bang pulses having an rf carrier, a receiver portionhaving a circuit for receiving echo signals, and means for connectingthe transmitter portion and the receiver portion to an antenna means,the combination therewith of: a reference oscillator for generating aclock reference signal; means coupled to detect the transmitter signaland coupled to receive the reference signal for detecting phasedifferences therebetween and for generating an error signal that isproportional to a function of the detected phase differences; meanscoupled to receive the error signal for storing the received errorsignal during the interpulse period; and means coupled to receive theclock reference signal and to receive the stored error signal for phaseshifting the clock reference signal in proportion to the error signalwhereby the reference signal is phase corrected relative to the carrierphase variation of each transmitted pulse signal.

5. In a radar circuit of the type including a transmitter portion havingrf oscillator means for generating and transmitting main bang pulses,and a receiver portion having a circuit for receiving and detecting echosignals, the combination therewith of: a stable oscillator forgenerating a reference signal; means coupled to receive a portion of thetransmitter signal and coupled to receive the reference signal fordetecting phase differences therebetween and for generating an errorsignal that is proportional to a function of the detected phasedifi'erences; means coupled to receive the error signal for storing thereceived error signal for an interpulse period; means coupled to receivethe reference signal and to receive the stored error signal for phaseshifting the reference signal in proportion to the error signal wherebythe reference signal is phase shifted relative to each transmittedsignal; and means coupled to receive the echo signal and the phaseshifted reference signal for continually detecting the phase differencetherebetween and for generating a coherent video signal.

6. In a radar circuit of the type including a transmitter section havinga pulsed rf oscillator means for generating and transmitting pulses, areceiver section having a circuit for detecting echo signals, and meansfor connecting the transmitter section and the receiver section to anantenna means, the combination therewith of: a reference oscillatormeans for generating two clock reference signals in phase quadraturewith one another; means coupled to receive a portion of the transmittedsignals and coupled to receive the reference signals for detecting phasedifferences between the transmitted signal and the two phase quadraturereference signals and for generating error signals which areproportional to functions of the phase differences therebetween; andmeans coupled to receive the reference signal and to receive the errorsignal for phase shifting the reference signal in proportion to theerror signal whereby the reference signal is phase corrected relative toeach transmitted signal.

7. In a radar circuit of the type including a transmitter section havinga pulsed rf oscillator means for generating and transmitting main bangpulses, a receiver section having a circuit for detecting echo signals,and means for connecting the transmitter section and the receiversection to an antenna means, the combination therewith of: a stablereference oscillator means for generating a reference signal; meanscoupled to receive a portion of the transmitter signals and coupled toreceive the reference signal for detecting phase difierences between thetransmitter signal and the reference signal and for generating twoin-phase quadrature error signals which are proportional to functions ofthe phase differences between the received signals; means coupled toreceive the error signals for storing the received error signals duringan interpulse period; and means coupled to receive the reference signaland to receive the error signals for phase shifting the reference signalin proportion to the error signal whereby the reference signal iscoherent relative to each transmitted signal.

8. In a radar circuit of the type including a transmitter section havinga pulsed rf oscillator, a receiver section having a circuit fordetecting echo signals, and means for connecting the transmitter sectionand the receiver section to an antenna means, the combination therewithof: reference oscillator means for generating two c-w reference signalsin phase quadrature with one another; means coupled to receive a portionof the transmitted signals and coupled to receive the reference signalsfor detecting phase differences between the transmitted signal and thetwo in-phase quadrature reference signals and for generating errorsignals which are proportional to the phase differences therebetween;means coupled to receive the reference signal and to receive the errorsignal for phase shifting the reference signal in proportion to theerror signal whereby the reference signal is phase corrected relative toeach transmitted signal; and means coupled to receive the echo signaland the phase shifted reference signal for continually phase detectingthe difference therebetween for generating a coherent video signaloutput.

9. A radar circuit comprising: a transmitter means having an rfoscillator for generating and transmitting pulsed signals; a receivermeans for detecting echo signals; a stable oscillator means forgenerating a c-w reference signal; means coupled to receive a portion ofthe transmitted signals and coupled to receive the reference signals fordetecting phase differences therebetween and for generating an errorsignal that is proportional to the phase differences therebetween; meanscoupled to receive the error signal for storing the received errorsignal for a predetermined period of time; and means coupled to receivethe c-w reference signal and to receive the error signal for phaseshifting the reference signal in proportion to the error signal wherebythe reference signal is phase corrected relative to each transmittedsignal.

10. A radar circuit comprising: a transmitter means having an rfoscillator for generating and transmitting pulsed signals; a receivermeans for detecting echo signals; an oscillator means for generating ac-w reference signal; means coupled to receive a portion of thetransmitted signals and coupled to receive the reference signals fordetecting phase differences therebetween and for generating an errorsignal that is proportional to the phase differences therebetween; meanscoupled to receive the error signal for holding the received errorsignal for an interpulse period; means coupled to receive the c-wreference signal and to receive the error signal for phase shifting thereference signal in proportion to the error signal whereby the referencesignal is phase corrected relative to each transmitted signal; and meanscoupled to receive the echo signal and to receive the phase shiftedreference signal for continually phase detecting the differencetherebetween for generating a coherent video signal output.

11. In a radar circuit of the type including a transmitter sectionhaving an rf oscillator, a receiver section having a circuit fordetecting echo signals, and means for connecting the transmitter sectionand the receiver section to an antenna means, the combination therewithof: an oscillator for generating an IF reference signal; means coupledto receive a portion of the transmitted signals at an IF level andcoupled to receive the IF reference signal for detecting phasedifferences between the transmitted signal and the reference signal andfor generating an error signal that is proportional to the phasedifferences therebetween; and means coupled to receive the IF referencesignal and to receive the error signal for phase shifting the IFreference signal in proportion to the error signal whereby the IFreference signal is phase corrected relative to each transmitted signal.

12. In a radar circuit of the type including a transmitter portionhaving an rf oscillator, a receiver portion having a circuit forreceiving and detecting echo signals, and means for connecting thetransmitter portion and the receiver portion to an antenna means, thecombination therewith of: an oscillator for generating an IF referencesignal; means coupled to receive a portion of the transmitted signal atIF level and to receive the IF reference signal for detecting phasedifferences therebetween and for generating an error signal that isproportional to the phase differences; means coupled to receive theerror signal for storing the received error signal for an-interpulseperiod; and means coupled to receive the IF reference signal and toreceive the stored error signal for phase shifting the IF referencesignal in proportion to the error signal whereby the IF reference signalis phase corrected relative to each transmitted signal.

13. In a radar circuit of the type including a transmitter portionhaving a pulsed rf oscillator, a receiver portion having a circuit forreceiving and detecting echo signals, and means for connecting thetransmitter portion and the receiver portion to an antenna means, thecombination therewith of: an oscillator for generating an IF referencesignal; means coupled to the receiver portion of the transmitted signalat IF level and coupled to receive the IF reference signal for detectingphase differences therebetween and for generating an error signal thatis proportional to the phase differences; means coupled to receive theIF reference signal and to receive the stored error signal for phaseshifting the IF reference signal in proportion to the error signalwhereby the IF reference signal is phase shifted relative to eachtransmitter signal; and means coupled to receive the echo signal at IFlevel and the phase shifted IF reference signal for continuallydetecting the phase difference therebetween and for generating acoherent video signal.

14. In a radar circuit of the type including a transmitter sectionhaving a pulsed rf oscillator, a receiver section having a circuit fordetecting echo signals, and means for connecting the transmitter sectionand the receiver section to an antenna means, the combination therewithof: a reference oscillator means for generating two IF reference signalsin quadrature with one another; means coupled to receive a portion ofthe transmitted signals at IF level and coupled to receive the IFreference signals for detecting phase differences between thetransmitted signal and the two in-quadrature reference signals and forgenerating error signals which are proportional to the phase differencestherebetween; and means coupled to receive the IF reference signal andto receive the error signal for phase shifting the IF reference signalin proportion to the error signal whereby the IF reference signal isphase corrected relative to each transmitted signal.

15. In a radar circuit of the type including a transmitter sectionhaving a pulsed rf oscillator, a receiver section having a circuit fordetecting echo signals, and means for connecting the transmitter sectionand the receiver section to an antenna means, the combination therewithof: a reference oscillator means for generating two IF reference signalsin quadrature with one another; means coupled to receive a portion ofthe transmitted signals at IF level and coupled to receive the IFreference signals for detecting phase differences between thetransmitted signal and the two in-quadrature reference signals and forgenerating error signals which are proportional to the phase differencestherebetween; means coupled to receive the error signal for storing thereceived error signal and for interpulse period; and means coupled toreceive the IF reference signal and to receive the error signal forphase shifting the IF reference signal in proportion to the error signalwhereby the IF reference signal is phase corrected relative to eachtransmitted signal.

16. In a radar circuit of the type including a transmitter sectionhaving a pulsed rf oscillator, a receiver section having a circuit fordetecting echo signals, and means for connecting the transmitter sectionand the receiver section to an antenna means, the combination therewithof: reference oscillator means for generating two c-w IF referencesignals in quadrature with one another; means coupled to receive aportion of the transmitted signals at IF level and coupled to receivethe IF reference signals for detecting phase differences between thetransmitted signal and the two in quadrature reference signals and forgenerating error signals which are proportional to the phase differencestherebetween; means coupled to receive the IF reference signal and toreceive the error signal for phase shifting the IF reference signal inproportion to the error signal whereby the IF reference signal is phasecorrected relative to each transmitted signal; and means coupled toreceive the echo signal at IF level and the phase shifted IF referencesignal for continually phase detecting the difference therebetween forgenerating a coherent video signal output.

17. In a radar circuit of the type including a transmitter sectionhaving a pulsed rf oscillator, a receiver section having a circuit fordetecting echo signals, and means for connecting the transmitter sectionand the receiver section to an antenna means, the combination therewithof: reference oscillator means for generating two c-w IF referencesignals in quadrature with one another; means coupled to receive aportion of the transmitted signals at IF level and coupled to receivethe IF reference signals for detecting phase differences which are rertional to the base diff therebetweerii 5338118 coupled to receive ill el l reference signal and to receive the error signal for phase shiftingthe IF reference signal in proportion to the error signal whereby the IFreference signal is phase corrected relative to each transmitted signal;means coupled to receive the error signal for storing the received errorsignal for an interpulse period; and means coupled to receive the echosignal at IF level and the phase shifted IF reference signal forcontinually phase detecting the difference therebetween for generating acoherent video signal output.

18. In a radar circuit of the type including a transmitted sectionhaving a circuit for generating and transmitting pulsed rf oscillatorysignals, and a receiver section having a circuit for detecting echosignals, the combination therewith of: a means for generating a clockreference signal; means coupled to receive a portion of the pulsed rfoscillatory signals generated at the transmitter and coupled to receivethe clock reference signal for detecting phase differences therebetween,and for generating an error signal that is proportional to a function ofthe detected phase differences; a stable local oscillator means in thereceiver section for generating a c-w output signal; phase shifter meanscoupled to receive the stable local oscillator output signal and toreceive the error signal for phase shifting the'local oscillator outputsignal to remove phase variations in the local oscillator output signalrelative to the transmitted signal resulting from rf starting phasevariations in the transmitted pulses; and means for receiving the echosignals and for receiving the phase shifted local oscillator signals forproducing a coherent echo signal.

19. In a radar circuit of the type including a transmitter sectionhaving a circuit for generating and transmitting pulsed rf oscillatorysignals, a receiver section having a circuit for detecting echo signals,the combination therewith of: a means for generating a clock referencesignal; means coupled to receive a portion of the pulsed rf oscillatorysignals generated by the transmitter and coupled to receive the clockreference signal for detecting phase differences between the transmittedsignal and the clock reference signal and for generating an error signalthat is proportional to a function of the detected phase differencestherebetween; means coupled to receive the error signal for storing thereceived error signal during the interpulsed period between transmittedpulse signals; a stable local oscillator means in the receiving sectionfor generating a c-w output signal; phase shifter means coupled toreceive the stable local oscillator output signal and to receive theerror signal for phase shifting the local oscillator output signal toremove phase variations in the local oscillator output signal relativeto the transmitted signal resulting from rf starting phase variations inthe transmitted pulses; andmeans for receiving the echo signals and forreceiving the phase shifted local oscillator signals for producing acoherent echo signal.

1. In a radar circuit of the type including a transmitter section havinga circuit for generating and transmitting a pulsed rf oscillatingsignal, a receiver section having a circuit for receiving and detectingecho signals, and means for connecting the transmitter section to andthe receiver section to an antenna means, the combination therewith of:a stable oscillator means for generating a reference signal; meanscoupled to receive a portion of the transmitter rf signals and coupledto receive the reference signal for measuring phase differencestherebetween and generating an error signal proportional to a functionof the measured phase differences; and means coupled to receive thereference signal and to receive the error signal for phase shifting thereference signal in proportion to the error signal for removing phasevariation between the reference signal and the transmitted pulseresulting from starting phase variations in the transmitted signalwhereby the reference signal is made coherent relative to each relatedecho signal.
 1. In a radar circuit of the type including a transmittersection having a circuit for generating and transmitting a pulsed rfoscillating signal, a receiver section having a circuit for receivingand detecting echo signals, and means for connecting the transmittersection to and the receiver section to an antenna means, the combinationtherewith of: a stable oscillator means for generating a referencesignal; means coupled to receive a portion of the transmitter rf signalsand coupled to receive the reference signal for measuring phasedifferences therebetween and generating an error signal proportional toa function of the measured phase differences; and means coupled toreceive the reference signal and to receive the error signal for phaseshifting the reference signal in proportion to the error signal forremoving phase variation between the reference signal and thetransmitted pulse resulting from starting phase variations in thetransmitted signal whereby the reference signal is made coherentrelative to each related echo signal.
 2. In a radar circuit of the typeincluding a transmitter section having a circuit for generating andtransmitting a pulsed rf oscillating signal, a receiver section having acircuit for receiving and detecting echo signals, and means forconnecting the transmitter section to and the receiver section to anantenna means, the combination therewith of: a means for generating aclock reference signal; means coupled to receive a portion of thetransmitter rf signals and coupled to receive the clock reference signalfor detecting phase differences between the transmitted signal and theclock reference signal and for generating an error signal that isproportional to a function of the detected phase differencestherebetween; and means coupled to receive the reference signal and toreceive the error signal for phase shifting the reference signal inproportion to the error signal for removing phase variation between theclock reference signal and the transmitted pulse resulting from startingphase variations in the transmitted signal whereby the reference signalis made coherent relative to each related echo signal.
 3. In a radarcircuit of the type including a transmitter portion having a circuit foRgenerating and transmitting main bang pulses having an rf carrier, areceiver portion having a circuit for receiving echo signals, and meansfor coupling the transmitter portion to and the receiver portion to anantenna means, the combination therewith of: a stable oscillator forgenerating a reference signal; means coupled to receive a portion of thetransmitter signals and to receive the reference signal for detectingphase differences therebetween and for generating an error signal thatis proportional to a function of the detected phase differences; meanscoupled to receive the error signal for storing the received errorsignal for a time period; and means coupled to receive the referencesignal and to receive the stored error signal for phase shifting thereference signal in proportion to the error signal to remove phasevariations in the reference signal relative to the transmitted signalwhereby the reference signal is made coherent relative to each relatedecho signal.
 4. In a radar circuit of the type including a transmitterportion for transmitting main bang pulses having an rf carrier, areceiver portion having a circuit for receiving echo signals, and meansfor connecting the transmitter portion and the receiver portion to anantenna means, the combination therewith of: a reference oscillator forgenerating a clock reference signal; means coupled to detect thetransmitter signal and coupled to receive the reference signal fordetecting phase differences therebetween and for generating an errorsignal that is proportional to a function of the detected phasedifferences; means coupled to receive the error signal for storing thereceived error signal during the interpulse period; and means coupled toreceive the clock reference signal and to receive the stored errorsignal for phase shifting the clock reference signal in proportion tothe error signal whereby the reference signal is phase correctedrelative to the carrier phase variation of each transmitted pulsesignal.
 5. In a radar circuit of the type including a transmitterportion having rf oscillator means for generating and transmitting mainbang pulses, and a receiver portion having a circuit for receiving anddetecting echo signals, the combination therewith of: a stableoscillator for generating a reference signal; means coupled to receive aportion of the transmitter signal and coupled to receive the referencesignal for detecting phase differences therebetween and for generatingan error signal that is proportional to a function of the detected phasedifferences; means coupled to receive the error signal for storing thereceived error signal for an interpulse period; means coupled to receivethe reference signal and to receive the stored error signal for phaseshifting the reference signal in proportion to the error signal wherebythe reference signal is phase shifted relative to each transmittedsignal; and means coupled to receive the echo signal and the phaseshifted reference signal for continually detecting the phase differencetherebetween and for generating a coherent video signal.
 6. In a radarcircuit of the type including a transmitter section having a pulsed rfoscillator means for generating and transmitting pulses, a receiversection having a circuit for detecting echo signals, and means forconnecting the transmitter section and the receiver section to anantenna means, the combination therewith of: a reference oscillatormeans for generating two clock reference signals in phase quadraturewith one another; means coupled to receive a portion of the transmittedsignals and coupled to receive the reference signals for detecting phasedifferences between the transmitted signal and the two phase quadraturereference signals and for generating error signals which areproportional to functions of the phase differences therebetween; andmeans coupled to receive the reference signal and to receive the errorsignal for phase shifting the reference signal in proportion to theerror signal Whereby the reference signal is phase corrected relative toeach transmitted signal.
 7. In a radar circuit of the type including atransmitter section having a pulsed rf oscillator means for generatingand transmitting main bang pulses, a receiver section having a circuitfor detecting echo signals, and means for connecting the transmittersection and the receiver section to an antenna means, the combinationtherewith of: a stable reference oscillator means for generating areference signal; means coupled to receive a portion of the transmittersignals and coupled to receive the reference signal for detecting phasedifferences between the transmitter signal and the reference signal andfor generating two in-phase quadrature error signals which areproportional to functions of the phase differences between the receivedsignals; means coupled to receive the error signals for storing thereceived error signals during an interpulse period; and means coupled toreceive the reference signal and to receive the error signals for phaseshifting the reference signal in proportion to the error signal wherebythe reference signal is coherent relative to each transmitted signal. 8.In a radar circuit of the type including a transmitter section having apulsed rf oscillator, a receiver section having a circuit for detectingecho signals, and means for connecting the transmitter section and thereceiver section to an antenna means, the combination therewith of:reference oscillator means for generating two c-w reference signals inphase quadrature with one another; means coupled to receive a portion ofthe transmitted signals and coupled to receive the reference signals fordetecting phase differences between the transmitted signal and the twoin-phase quadrature reference signals and for generating error signalswhich are proportional to the phase differences therebetween; meanscoupled to receive the reference signal and to receive the error signalfor phase shifting the reference signal in proportion to the errorsignal whereby the reference signal is phase corrected relative to eachtransmitted signal; and means coupled to receive the echo signal and thephase shifted reference signal for continually phase detecting thedifference therebetween for generating a coherent video signal output.9. A radar circuit comprising: a transmitter means having an rfoscillator for generating and transmitting pulsed signals; a receivermeans for detecting echo signals; a stable oscillator means forgenerating a c-w reference signal; means coupled to receive a portion ofthe transmitted signals and coupled to receive the reference signals fordetecting phase differences therebetween and for generating an errorsignal that is proportional to the phase differences therebetween; meanscoupled to receive the error signal for storing the received errorsignal for a predetermined period of time; and means coupled to receivethe c-w reference signal and to receive the error signal for phaseshifting the reference signal in proportion to the error signal wherebythe reference signal is phase corrected relative to each transmittedsignal.
 10. A radar circuit comprising: a transmitter means having an rfoscillator for generating and transmitting pulsed signals; a receivermeans for detecting echo signals; an oscillator means for generating ac-w reference signal; means coupled to receive a portion of thetransmitted signals and coupled to receive the reference signals fordetecting phase differences therebetween and for generating an errorsignal that is proportional to the phase differences therebetween; meanscoupled to receive the error signal for holding the received errorsignal for an interpulse period; means coupled to receive the c-wreference signal and to receive the error signal for phase shifting thereference signal in proportion to the error signal whereby the referencesignal is phase corrected relative to each transmitted signal; and meanscoupled to receive the echo signal aNd to receive the phase shiftedreference signal for continually phase detecting the differencetherebetween for generating a coherent video signal output.
 11. In aradar circuit of the type including a transmitter section having an rfoscillator, a receiver section having a circuit for detecting echosignals, and means for connecting the transmitter section and thereceiver section to an antenna means, the combination therewith of: anoscillator for generating an IF reference signal; means coupled toreceive a portion of the transmitted signals at an IF level and coupledto receive the IF reference signal for detecting phase differencesbetween the transmitted signal and the reference signal and forgenerating an error signal that is proportional to the phase differencestherebetween; and means coupled to receive the IF reference signal andto receive the error signal for phase shifting the IF reference signalin proportion to the error signal whereby the IF reference signal isphase corrected relative to each transmitted signal.
 12. In a radarcircuit of the type including a transmitter portion having an rfoscillator, a receiver portion having a circuit for receiving anddetecting echo signals, and means for connecting the transmitter portionand the receiver portion to an antenna means, the combination therewithof: an oscillator for generating an IF reference signal; means coupledto receive a portion of the transmitted signal at IF level and toreceive the IF reference signal for detecting phase differencestherebetween and for generating an error signal that is proportional tothe phase differences; means coupled to receive the error signal forstoring the received error signal for an interpulse period; and meanscoupled to receive the IF reference signal and to receive the storederror signal for phase shifting the IF reference signal in proportion tothe error signal whereby the IF reference signal is phase correctedrelative to each transmitted signal.
 13. In a radar circuit of the typeincluding a transmitter portion having a pulsed rf oscillator, areceiver portion having a circuit for receiving and detecting echosignals, and means for connecting the transmitter portion and thereceiver portion to an antenna means, the combination therewith of: anoscillator for generating an IF reference signal; means coupled to thereceiver portion of the transmitted signal at IF level and coupled toreceive the IF reference signal for detecting phase differencestherebetween and for generating an error signal that is proportional tothe phase differences; means coupled to receive the IF reference signaland to receive the stored error signal for phase shifting the IFreference signal in proportion to the error signal whereby the IFreference signal is phase shifted relative to each transmitter signal;and means coupled to receive the echo signal at IF level and the phaseshifted IF reference signal for continually detecting the phasedifference therebetween and for generating a coherent video signal. 14.In a radar circuit of the type including a transmitter section having apulsed rf oscillator, a receiver section having a circuit for detectingecho signals, and means for connecting the transmitter section and thereceiver section to an antenna means, the combination therewith of: areference oscillator means for generating two IF reference signals inquadrature with one another; means coupled to receive a portion of thetransmitted signals at IF level and coupled to receive the IF referencesignals for detecting phase differences between the transmitted signaland the two in-quadrature reference signals and for generating errorsignals which are proportional to the phase differences therebetween;and means coupled to receive the IF reference signal and to receive theerror signal for phase shifting the IF reference signal in proportion tothe error signal whereby the IF reference signal is phase correcteDrelative to each transmitted signal.
 15. In a radar circuit of the typeincluding a transmitter section having a pulsed rf oscillator, areceiver section having a circuit for detecting echo signals, and meansfor connecting the transmitter section and the receiver section to anantenna means, the combination therewith of: a reference oscillatormeans for generating two IF reference signals in quadrature with oneanother; means coupled to receive a portion of the transmitted signalsat IF level and coupled to receive the IF reference signals fordetecting phase differences between the transmitted signal and the twoin-quadrature reference signals and for generating error signals whichare proportional to the phase differences therebetween; means coupled toreceive the error signal for storing the received error signal and forinterpulse period; and means coupled to receive the IF reference signaland to receive the error signal for phase shifting the IF referencesignal in proportion to the error signal whereby the IF reference signalis phase corrected relative to each transmitted signal.
 16. In a radarcircuit of the type including a transmitter section having a pulsed rfoscillator, a receiver section having a circuit for detecting echosignals, and means for connecting the transmitter section and thereceiver section to an antenna means, the combination therewith of:reference oscillator means for generating two c-w IF reference signalsin quadrature with one another; means coupled to receive a portion ofthe transmitted signals at IF level and coupled to receive the IFreference signals for detecting phase differences between thetransmitted signal and the two in quadrature reference signals and forgenerating error signals which are proportional to the phase differencestherebetween; means coupled to receive the IF reference signal and toreceive the error signal for phase shifting the IF reference signal inproportion to the error signal whereby the IF reference signal is phasecorrected relative to each transmitted signal; and means coupled toreceive the echo signal at IF level and the phase shifted IF referencesignal for continually phase detecting the difference therebetween forgenerating a coherent video signal output.
 17. In a radar circuit of thetype including a transmitter section having a pulsed rf oscillator, areceiver section having a circuit for detecting echo signals, and meansfor connecting the transmitter section and the receiver section to anantenna means, the combination therewith of: reference oscillator meansfor generating two c-w IF reference signals in quadrature with oneanother; means coupled to receive a portion of the transmitted signalsat IF level and coupled to receive the IF reference signals fordetecting phase differences between the transmitted signal and the twoin quadrature reference signals and for generating error signals whichare proportional to the phase differences therebetween; means coupled toreceive the IF reference signal and to receive the error signal forphase shifting the IF reference signal in proportion to the error signalwhereby the IF reference signal is phase corrected relative to eachtransmitted signal; means coupled to receive the error signal forstoring the received error signal for an interpulse period; and meanscoupled to receive the echo signal at IF level and the phase shifted IFreference signal for continually phase detecting the differencetherebetween for generating a coherent video signal output.
 18. In aradar circuit of the type including a transmitted section having acircuit for generating and transmitting pulsed rf oscillatory signals,and a receiver section having a circuit for detecting echo signals, thecombination therewith of: a means for generating a clock referencesignal; means coupled to receive a portion of the pulsed rf oscillatorysignals generated at the transmitter and coupled to receive the clockreference siGnal for detecting phase differences therebetween, and forgenerating an error signal that is proportional to a function of thedetected phase differences; a stable local oscillator means in thereceiver section for generating a c-w output signal; phase shifter meanscoupled to receive the stable local oscillator output signal and toreceive the error signal for phase shifting the local oscillator outputsignal to remove phase variations in the local oscillator output signalrelative to the transmitted signal resulting from rf starting phasevariations in the transmitted pulses; and means for receiving the echosignals and for receiving the phase shifted local oscillator signals forproducing a coherent echo signal.